To realize the length to diameter ratios when BTA deep hole drilling long and slender tool-systems, consisting of drill head and boring bar are used, which have low dynamic torque and bending stiffnesses. Due to the low rigidity, process disturbances can occur during BTA drilling, which can jeopardize process reliability and process stability. Possible consequences of this instability can be increased tool wear, high noise emission and unusable workpieces. In earlier studies, mostly torsional and bending vibrations were analyzed. In this work, the measured vibrations in the longitudinal direction/feed direction are investigated to estimate an influence on the process stability.

When bores with high length-to-diameter ratios (l/D > 10) and large diameters (D > 40 mm) are required, usually, the Boring and Trepanning Association (BTA) deep hole drilling process is used. Common industrial applications of this process are aerospace engineering and petrol exploration, where drilled components range from landing gears and engine shafts to drill collars. Since such parts tend to be particularly costly and highly safety–critical, ensuring favorable surface integrity during drilling is crucial to guarantee their reliability and performance. This study aims to identify correlations between the BTA deep hole drilling process and the resulting surface integrity using experimental and simulative approaches. The impact of feed and cutting speed on the thermomechanical loads and the resulting surface integrity are analyzed, also taking into account the occurrence of dynamic process disturbances. Particularly, the formation of white etching layers (WEL) is investigated using well-established, conventional techniques such as optical microscopy and microhardness testing. Additionally, innovative micromagnetic methods are employed. Magnetic Barkhausen noise (MBN) analysis is qualified as a well-applicable approach for rapid, non-destructive detection of WEL. To enhance understanding of MBN analysis and increase its robustness, the underlying mechanisms, governing the magnetic behavior of the subsurface are elucidated in detail by X-ray diffraction (XRD), electron backscatter diffraction (EBSD), magnetic force microscopy (MFM) and magneto-optical Kerr effect (MOKE) microscopy. The methodology will serve as a basis for controlled subsurface conditioning in BTA deep hole drilling.

The reliable detection and precise assessment of white etching layers (WEL) are key challenges in the investigation of a component's surface integrity. This paper proposes an innovative methodology for evaluating the extent of WEL in quenched and tempered steels, machined by Boring and Trepanning Association (BTA) deep hole drilling. Micrographs obtained by light microscopy were partitioned into classes by three methods, separating the WEL from the base material and the embedding resin. Traditional manual segmentation was performed as a benchmark for automatic segmentation methods. A gray level thresholding-based method served for the segmentation of micrographs partitioned into subsets. In addition to conventional manual and thresholding-based segmentation, a machine learning-based approach for image segmentation was applied. The segmented images were further analyzed by a newly developed set of algorithms, implemented to obtain detailed information on the WEL, e.g. their average thickness as well as the area covered by WEL in the micrographs. Results indicate that both, gray level thresholding, as well as machine learning-based image segmentation, show potential for the automated diagnosis and assessment of WEL. They both yield quantitatively similar, but less biased results compared to manual segmentation. (c) 2024 The Authors. Published by Elsevier B.V.

The BTA deep hole drilling process is applied in order to produce bores with a large length to diameter ration at comparably high diameters of the bores. During drilling, first, the bore is cut by the cutting edge and shortly after that, a guide pad slides over the newly produced bore wall, burnishing the surface. These two effects condition the bore wall and alter its surface integrity depending on the process parameters. In the past, extensive destructive and non-destructive tests were conducted to obtain information on the surface integrity of the machined parts. Furthermore, a large number of in- and off-process measurements were carried out in material and cost-intensive experiments to determine values such as residual stresses or white etching layers. The presented work shows different finite element models of the BTA deep hole drilling process using continuous remeshing and, in order to reduce the calculation times, the Coupled Eulerian-Lagrangian (CEL) method as well. The results simulated based on this models comprise temperatures, process forces and surface properties that are compared to measured values from pervious works for validation. The various approaches are evaluated to determine whether they predict the bore hole surface integrity and thus support future investigations. (c) 2024 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0)

In BTA (Boring and Trepanning Association) deep hole drilling the resulting surface and subsurface zone of the bore are conditioned by two main components of the tool, the cutting edge and the guide pads. To differentiate the influence of the components, experiments in an analogue model setup were conducted only using the cutting edge. Different cutting edge designs and process parameters were used during the machining experiments to determine the influence on the surface integrity. Using non-destructive measurement techniques, the specimens were analyzed regarding the residual stress state and the surface roughness. The model-experiment-based results are compared to investigations of the surface integrity in original BTA deep hole drilling.

For many years, tool wear has been a critical issue with respect to productivity, cost, and part quality, particularly for superalloy machining. The underlying wear mechanisms of a new turning tool, FreeTurn, is revealed in this paper towards its potential for a more sustainable way of metal cutting. It is a specially designed turning tool that is held by the tool spindle and has a working plane perpendicular to the centreline of the tool spindle, making it rotatable on its working plane. Owing to the unique feature of FreeTurn compared with conventional turning tools, the focus of this study is on the effect of dynamic tool–workpiece engagement on tool wear. The tool path strategy is first set to achieve a cylindrical surface in longitudinal turning with a rotatable FreeTurn tool. Series of experiments with different tool path strategies are performed on a turn–milling machine, using Inconel 718 as an example of workpiece material. The results indicate that the coupling effect between notch and flank wear is the decisive factor of tool wear in free turning with respect to its rotation and feeding directions. While the tool wear can be significantly reduced if the tool feeds with increasing cutting edge angle, the tool will soon be worn out if it feeds with decreasing cutting edge angle. Tool rotation in free turning plays a key role in reducing adhesion on the cutting tool and increasing the tool rotation speed can further improve this effect. Additionally, a more sustainable solution that uses both sides of the cutting edge becomes possible with FreeTurn as well, improving the tool utilisation. The results demonstrate considerable guiding significance for exploring the potential of this new turning tool towards a longer tool life.

In-process measurements are often used to gain information and increase the understanding of the machining process. Furthermore, these measurements can be used to control the process during machining. In processes such as milling or turning the sensors and measuring devices can often be placed inside the working area of the machine or attached to the tool and observe the contact area between tool and workpiece. The contact area of processes such as drilling, boring or BTA (Boring and Trepanning Association) deep hole drilling is inaccessible from the outside. The BTA process is a deep hole drilling method used mainly for machining relatively large diameters in complex and cost-intensive parts often at the end of the value chain. The resulting bore surfaces of these parts are often highly stressed and are commonly subjected to post-processing. With sufcient information about the process and the produced surface integrity of the bore, this post-processing could be reduced or even omitted. In order to get information about the contact area or the resulting surface of the bore, without destroying the workpiece, sensors need to be implemented into the tool in order to measure from inside the bore. The challenges in the design process of the drill head modifcations and the implementation of two diferent sensor systems are discussed in this paper. Furthermore, the manufacturing and application of the modified BTA drill heads are described. Finally, the results from cutting tests on one of the modified drill heads are presented.

The BTA deep hole drilling process is used to machine deep bores with a large diameter. The cutting process, consisting of the material removal by cutting edge and the surface burnishing by the guidepads influence the surface of the bore. To separate the impact of the cutting edge from that of the guidepads on the surface of the bore and the subsurface zone an experimental model setup in analogy to the BTA process was developed. This paper covers the differences to the conventional BTA deep hole drilling, the experimental boundary conditions and the measurement of the surface roughness. The results are compared to previous analysis of the surface integrity of BTA deep hole drilled specimens. Furthermore, conclusions about the process forces are drawn from the documented loads occurring for the machine axes. In part 2 of this study, the surface integrity of the specimens is further analyzed using destructive and non-destructive methods.

(Mikro-) Magnetische Prüfsysteme werden zur schnellen und zerstörungsfreien Charakterisierung von Oberflächenrandzonen BTA-tiefgebohrter Komponenten eingesetzt. Zur Erhöhung der Robustheit der Prüfmethodik erfolgen Analysen der Störgrößen sowie Validierungsmessungen mit verschiedenen Prüfsystemen und Sensoriken. Die Untersuchungen sind Teil der Entwicklung einer Softsensorik, die im Rahmen einer robusten Prozessregelung die gezielte Oberflächenkonditionierung beim Tiefbohren ermöglichen wird. (Micro-) Magnetic testing systems are employed for the fast and non-destructive characterization of subsurface zones of BTA deep drilled components. To increase the robustness of the methodology, an analysis of disturbance variables is carried out and validation measurements are performed, using different testing systems and sensors. The experiments are part of the development of a soft sensor for robust process control, which will allow for the targeted conditioning of surfaces in deep hole drilling.

To machine bores with larger diameters (D > 40mm) and a length to diameter ratio greater than ten (lb/D > 10) the BTA deep hole drilling process is often used. The cutting action of the cutting edge and the burnishing of the guide pads influence the resulting surface and the subsurface zone of the machined bore. The guide pads support the BTA drill head against the machined bore to prevent straightness deviations. A thermo-mechanical load, which results from the cutting and burnishing, influences the surface of the bore and effects the surface integrity, i.e. micro hardness, residual stress state, microstructure or the surface roughness, of the bore. In this paper, a measurement strategy to determine the thermal load in the subsurface zone using thermocouples is presented. Furthermore, a fiber-optic ratio pyrometer was used to measure the temperature in the contact zone between the cutting edge and the wall of the bore. The experiments were carried out using different workpiece materials, tool coatings and cutting parameters. The measurements are analyzed and set in context with previous studies.

Based on the process design, presented in part 1, the impact of feed and cutting speed on residual stress, microstructure and microhardness in the subsurface zone of the bores is analyzed. The formation of residual stresses is found to depend significantly on the selection of cutting parameters. When using high feed rates, white etching layers (WEL) are observed in the subsurface zone of the bores. These layers have an increased hardness and, in some cases, tensile residual stresses. Magnetic Barkhausen noise (MBN) is successfully applied for the non-destructive, efficient and reliable WEL detection.

The aircraft landing gear and its associated systems represent a compelling design challenge: simultaneously a system, a structure, and a machine, it supports the aircraft on the ground, absorbs landing and braking energy, permits maneuvering, and retracts to minimize aircraft drag. Yet, as it is not required during flight, it also represents dead weight and significant effort must be made to minimize its total mass. The Design of Aircraft Landing Gear, written by R. Kyle Schmidt, PE (B.A.Sc. - Mechanical Engineering, M.Sc. - Safety and Aircraft Accident Investigation, Chairman of the SAE A-5 Committee on Aircraft Landing Gear), is designed to guide the reader through the key principles of landing system design and to provide additional references when available. Many problems which must be confronted have already been addressed by others in the past, but the information is not known or shared, leading to the observation that there are few new problems, but many new people. The Design of Aircraft Landing Gear is intended to share much of the existing information and provide avenues for further exploration. The design of an aircraft and its associated systems, including the landing system, involves iterative loops as the impact of each modification to a system or component is evaluated against the whole. It is rare to find that the lightest possible landing gear represents the best solution for the aircraft: the lightest landing gear may require attachment structures which don't exist and which would require significant weight and compromise on the part of the airframe structure design. With those requirements and compromises in mind,The Design of Aircraft Landing Gear starts with the study of airfield compatibility, aircraft stability on the ground, the correct choice of tires, followed by discussion of brakes, wheels, and brake control systems. Various landing gear architectures are investigated together with the details of shock absorber designs. Retraction, kinematics, and mechanisms are studied as well as possible actuation approaches. Detailed information on the various hydraulic and electric services commonly found on aircraft, and system elements such as dressings, lighting, and steering are also reviewed. Detail design points, the process of analysis, and a review of the relevant requirements and regulations round out the book content. The Design of Aircraft Landing Gear is a landmark work in the industry, and a must-read for any engineer interested in updating specific skills and students preparing for an exciting career.

Der Beitrag befasst sich mit Teilaspekten bei der Entwicklung von Methoden zur gezielten, bearbeitungsparallelen Oberflächenkonditionierung beim Tiefbohren. Konkret handelt es sich um messtechnische und simulationsbasierte Ansätze zur Identifikation von thermomechanischen Prozesszuständen beim BTA- und ELB-Verfahren. Hierbei werden Möglichkeiten zur Gewinnung von Prozessdaten sowohl mit einer in-situ eingesetzten Sensorik als auch mit begleitend durchgeführten FEM-Simulationen betrachtet. Diese Daten bilden die Grundlage einer Prozessregelung für die beiden Tiefbohrverfahren. Im zweiten Teil werden nun die Arbeiten und Ergebnisse zum ELB-Tiefbohren behandelt.   The article deals with aspects of developing methods specifically for surface conditioning in deep hole drilling parallel to machining. This involves metrological and simulation-based approaches for identifying thermo-mechanical process conditions in both BTA and ELB process. Ways for obtaining process data both with sensor technology used in-situ and with FEM simulations performed concomitantly are investigated. These data form the basis of a deep hole process control. The second part presents the work and the results on single lip deep hole drilling.

Der Beitrag befasst sich mit Teilaspekten bei der Entwicklung von Methoden zur gezielten, bearbeitungsparallelen Oberflächenkonditionierung beim Tiefbohren. Konkret handelt es sich um messtechnische und simulationsbasierte Ansätze zur Identifikation von thermomechanischen Prozesszuständen beim BTA- und ELB-Verfahren. Hierbei werden Möglichkeiten zur Gewinnung von Prozessdaten sowohl mit einer in-situ eingesetzten Sensorik als auch mit begleitend durchgeführten FEM-Simulationen betrachtet. Diese Daten bilden die Grundlage einer Prozessregelung für die beiden Tiefbohrverfahren. Im ersten Teil werden zunächst die Arbeiten und Ergebnisse zum BTA-Tiefbohren behandelt.   The article deals with aspects of developing methods specifically for surface conditioning in deep hole drilling parallel to machining. This involves metrological and simulation-based approaches for identifying thermo-mechanical process conditions in both BTA and ELB process. Ways for obtaining process data both with sensor technology used in-situ and with FEM simulations performed concomitantly are investigated. These data form the basis of a deep hole process control. The first part presents the work and the results on BTA deep hole drilling.

The BTA (Boring and Trepanning Association) deep-hole drilling process is used to machine bores with large diameters (D > 40 mm) and a bore-length (l) to diameter ratio lager than ten (l/D >10). The resulting bore surface and its sub-surface zone are influenced by the cutting action and the self-guiding effect of the tool. The Guide pads support the asymmetric tool on the bore surface while burnishing the surface. The mechanical/thermal loads induced by the process lead to hardening, microstructure alteration and substantial residual stresses in the sub-surface. Particularly the residual stress state influences the fatigue strength and reliability of the machined part. To predict the residual stress in BTA deep-hole drilling, for the first time a novel analytical modeling approach is developed based on eigenstrain theory, integrating the machining process of cutting insert and the burnishing process of guide pad. A semi-analytical 3D contact model is built for the cycling incremental plasticity due to the equivalent mechanical/thermal loading of cutting process. Furthermore, an approximate estimation is provided for the contact condition between the inclined guide pad and bore hole, which facilitates the incremental contact analysis in the burnishing process. With the induced inelastic deformation known, residual stress distribution in the machined surface is constructed based on the eigenstrain theory. The results of the model are compared to X-Ray-Diffraction (XRD) measurements of BTA deep-hole drilled specimens.

Mechanical properties of BTA deep drilled components made of AISI 4140+QT under quasi-static loading are analyzed in instrumented compression tests, inspired by the tube-flattening test according to DIN EN ISO 8492. Digital image correlation (DIC) analysis is used to observe spatial strain distribution on the front side of specimens during compression. It is found that microstructural changes resulting from drilling, particularly the formation of white etching layers (WEL), play a key role in the loading capability of the components under compression. Higher forces needed to be applied to compress specimens with WEL and crack initiation was observed at lower displacements.

Abstract In this study, the influence of cutting speed and feed rate on surface integrity in Boring Trepanning Association (BTA) deep hole drilling of AISI 4140+QT is investigated. Microstructure and micro-hardness in the subsurface zones of bores are analyzed, using metallographic and micromagnetic methods. It was found that when using high feed rates and cutting speeds, white etching layers (WEL) form at the surface of the bores. These layers are up to three times harder than the substrate material and have a maximum thickness of approx. t WEL ≈ 12 µm{t_{\mathrm{WEL}}}\approx 12\hspace{0.1667em}\text{\textmu m}. WEL were usually followed by a transitional layer, so that elevated hardness was observed until a depth of d surf = 35 µm{d_{\mathrm{surf}}}=35\hspace{0.1667em}\text{\textmu m} below the surface. Magnetic Barkhausen noise (MBN) analysis proved to be applicable for the fast and reliable detection of WEL. The presented results contribute to gaining a deeper understanding of the complex interrelations between the design of the BTA process, the resulting microstructure in the machined component and the properties of the conditioned surface. Based on discovered correlations, a dynamic process control will be developed for BTA deep hole drilling, which will allow reliably tailoring surface integrity of components to specific demands, like an optimized fatigue performance.

The relationship between the cutting speed, the feed, the resulting process forces during the BTA deep hole-drilling process and the functional properties in the bore sub-surface zone of AISI 4140 and AISI 304 L is analysed. Due to the asymmetric design of the drill head radial forces occur which are supported through guide pads on bore surface. The result is an inner force flow inside the tool that affects a self-guiding effect during the drilling process. Due to this process the bore (sub-)surface zone is impinged with thermal and mechanical loads resulting in hardening, structural changes in microstructure and the occurrence of residual stresses, which can influence the fatigue strength, service life or reliability of the part. Residual stresses are measured using the magnetic Barkhausen noise method. Understanding the relationship between the process forces and functional properties in the bore sub-surface zone is essential for a following process control in order to generate defined bore sub-surface zones.